I've done it both ways. It's whatever you prefer. You may want to do the online signup process though. I can't remember if it would let me sign up and pay the first bill that way, or if there was a bit of an approval wait period involved. Regardless, it wasn't a long wait period. Just don't wait to pay online the last day without checking first. Once you're signed up, it's a fast way of paying.
I set mine up for them to auto take it out of my checking. No fuss no muss. Online works the same, I just don't do the work. They did the paperwork for the auto checking withdrawal.....
Of course it's more convinient if you pay online or setup autopay.... Plus, you don't have to worry about your mail getting lost (happened to me twice!!!)